1. Field of the Invention
The present invention relates to a projector having an electronic whiteboard function, an electronic whiteboard system using the projector, and a method of acquiring an indicated point in the electronic whiteboard system.
2. Description of the Related Art
A coordinate input device made available on the market in recent years has a combination of a signal processor including two ultrasonic wave receivers and one infrared ray receiver with an electronic pen including an infrared ray emitter and an ultrasonic wave generator. This coordinate input device is one implementation of an electronic whiteboard function which measures the distances from the electronic pen to the two ultrasonic wave receivers of the removable signal processor mounted on a whiteboard or the like to acquire the position of the electronic pen, and takes the coordinates of the electronic pen position into a personal computer.
In the foregoing implementation, the signal processor is first mounted near a corner of the whiteboard. An image generated by a personal computer is projected onto the whiteboard by a projector. Particular positions on the projected image (for example, four corners) are specified by the electronic pen to store the positions on the projected image in the signal processor. Subsequently, the coordinates are calculated by comparing the position of the electronic pen with the previously stored particular positions, and the calculated coordinates are passed to the personal computer for moving a mouse cursor or the like.
The operation of the foregoing electronic whiteboard system will be described with reference to FIGS. 1A, 1B. As illustrated in FIG. 1A, signal processor 2 mounted on whiteboard 1 comprises infrared ray receiver 20, ultrasonic wave receiver 21, and ultrasonic wave receiver 22. Electronic pen 3 simultaneously emits infrared ray pulse 4 and ultrasonic pulse 5 (the pulse used herein refers to a signal which is only instantaneously generated). Then, taking advantage of the principle of finding the distance to lightning by measuring a time period from the time the lightning is seen to the time associated thunder is heard, signal processor 2 can know the distances from electronic pen 3 to ultrasonic wave receivers 21, 22 by measuring time periods from the time infrared pulse 4 impinges on infrared ray receiver 20 to the time ultrasonic waves impinge on ultrasonic wave receivers 21, 22. Since ultrasonic wave receivers 21, 22 are fixed on signal processor 2, the position of electronic pen 3 viewed from ultrasonic wave receivers 21, 22 can be found from the principle of triangulation (the position of a certain point can be calculated if the distances from different two points to the certain point are known).
Bearing the foregoing in mind, as illustrated in FIG. 1B, an image is projected onto a whiteboard from a projector, and upper left corner 61, upper right corner 62, lower left corner 63, and lower right corner 64 are specified by electronic pen 3 on the projected image 6 to store the position of projected image 6 in signal processor 2 (initialization of coordinates). Subsequently, when electronic pen 3 is used within projected image 6, the position of electronic pen 3 on image 6 can be calculated by comparing the position of the projected image with electronic pen 3. As a result, the coordinates of electronic pen 3 can be delivered to a personal computer, the mouse cursor can be moved over image 6, an icon oh the screen can be specified by electronic pen 3, and so on.
There is another exemplary electronic whiteboard which eliminates the initialization by installing a plurality of ultrasonic wave receivers at the corners of a writing surface on a whiteboard (see, for example, Japanese Patent Laid-open Publication No. 333314/2002 (page 3, FIG. 5) and Japanese Patent Laid-open Publication No. 125736/2001 (pages 3-13, FIG. 1)).
However, in the prior art example which involves the initialization of the coordinates, the burdensome initialization is required for every change in the position and/or distance of projection from the projector to the whiteboard.
On the other hand, in the prior art examples described in Japanese Patent Laid-open Publication No. 333314/2002 and Japanese Patent Laid-open Publication No. 125736/2001 which can omit the initialization by mounting a plurality of ultrasonic wave receivers, which define positional references, at the corners of the writing surface on the whiteboard, unless the sides of a projected image are fitted to the ends of the writing surface, the coordinates on the writing surface does not match the coordinates of the projected image. Inconveniently, this entails requirements for fixing the position and angle with which the projector projects images onto the whiteboard, or for readjusting the projecting conditions for each projection. The aforementioned signal processor is advantageous in that it can be mounted on any wall surface, and the projector can freely project images of any desired sizes as well.
The prior art examples described in JP-2002-333314-A and JP-2001-125736-A spoil the foregoing freedom.